Knowledge of individual differences in xenobiotic exposure, uptake, and metabolism in the skin, and the potential value for exposure assessment of individual health effects is limited. This reduces our ability to investigate the correlation between individual factors that affect dermal exposure and limits the use of dermal exposure assessment and its relationship to systemic exposure from other routes, compromising overall exposure assessment. We propose to test several hypotheses: (1) keratinocytes of the viable epidermis metabolize polycyclic aromatic hydrocarbons (PAH) to electrophiles through the induction of the cytochrome P450 oxygenases that adduct nucleophilic residues of keratin expressed during differentiation and maturation, (2) PAH exposure to the epidermis results in an individual pattern of expression of genes and their corresponding proteins; (3) PAH induced changes in gene expression in the epidermis correlate with exposure level and, thus, can predict individual differences in the dose response to PAH exposure. We will determine and characterize the response in the reconstructed human epidermis and human skin cells to PAH exposure. Specifically, we will identify the cells that express phase 1 and phase 2 enzymes, which metabolize PAH, and the environmentally responsive genes which may modify individual response to the PAH exposure. Secondly, we will determine if the concentration of PAH-electrophile adducted keratin in reconstructed epidermis exposed to known levels of PAH correlates with PAH exposure in a dose-responsive manner and establish if keratin adducts may be used as quantitative biomarkers of dermal exposure to PAH. Third, we will determine the pattern of gene and protein expression in the epidermis that are critical to PAH-exposure response and to quantitative differences in response to exposure levels that correlate, and, thus, predict individual differences. Finally, where statistically significant individual differences are observed, we will genotype candidate genes for allelic differences in environmentally responsive genes that may be responsible for these quantitative differences. The potential significant differences in individual metabolism and gene expression in the epidermis in response to PAH exposure and macromolecule adduction and/or damage, which may exist in the human population, require characterization and inclusion into exposure and risk assessment models. The results obtained by these proposed studies will increase our knowledge of the role of dermal exposure and the internal dose received to both the skin and internal tissues.